Conventional integrated circuits are configured with one or more dies disposed in the integrated circuit package. Sometimes, it is desirable to have multiple functions on an integrated circuit that are difficult to fabricate on a single die. The reason for this is that some processes are not compatible, such as a low voltage CMOS process and a high voltage CMOS process. It is sometimes easier to utilize two different die for this operation (also requiring different wafers fabricated with different processes). Sometimes, a low voltage process is utilized to fabricate a microcontroller unit that has both analog and digital functionalities associated therewith and, when utilized in a high voltage application such as a power supply controller, it is desirable to have contained within the same package driving transistors. These driving transistors are typically processed with a higher voltage process and it is easier to utilize two die in the package as opposed to attempting to fabricate the entire structure on a single integrated circuit.
Another reason to utilize two die is to facilitate diversity among an offered product line. It may be desirable, for example, to provide multiple memory options for a packaged device and, rather than manufacturing single die devices, each with a separate memory capacity which requires multiple different wafers, it may be easier to merely utilize a common microcontroller design and combine it with different memory chips in a single package device utilizing multiple die. This, of course, depends upon demand. Another reason to use multiple die is when a controller unit utilized in a power supply application. In this application, pulse width modulation techniques are utilized requiring driving transistors to drive the magnetics. In this situation, it is desirable to add both the controller function and the driving function in a single package device. These driving transistors are high voltage transistors that are typically not compatible with a process for manufacturing the controller. It is relatively easy to provide an option to a customer in a very timely manner by merely utilizing discrete transistor die within a package and use bond wires to interface these die with the controller die.
Another reason to utilize multiple die is to increase the number of channels for a multi-channel device. It may be that the die is designed with two channels of operation, these being RF channels or analog channels or even digital channels such as used in an isolator. Driver circuits could also be implemented in such a manner. If the die is manufactured with four channels, offering an 8 channel device or a 6 channel device would require either developing a separate die with that many channels or a large die with 8 channels that has only a small number of channels bonded out in one configuration and all channels bonded out in another configuration. However, a 4 channel device can be manufactured, for example, to provide 1 to 4 channels with a single die package or 6 to 8 channels with a two die device.
The problem with providing multiple die is that each die must have a separate power and ground supply connection in addition to possibly some bond out options for configuring the device. This requires an additional VDD for each chip, and mounting two die requires a large area.